Color television



Sept. 4, 1951 G. c. szlKLAl 2,567,040

COLOR TELEVISION Filed Dec. 26, 1947 2 Sheets-Sheer, 1

t aLl/f if; 655ML f WH/VIVE( Ey., fra/wf Sept. 4, 1951 Filed Deo. 26, 1947 G. C. SZIKLAI COLOR TELEVISION 2 Sheets-Sheet 2 Patented Sept. 4, 1951 coLoR TELEVISION v George C. Sziklai, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 26, 1947, Serial No. 793,932

This invention relates to color television, and more particularly to methods and apparatus for the transmission of color television images in a simultaneous manner by the color additive process.

It has been reasonably well established in the art of colorimetry that substantially all colors can be visually simulated in reproduction by the addition in proper proportions of brightness of three primary or selected component colors. The three component colors will, for the purpose of brevity and example, be hereafter referred to as red,- green and blue.

In color television, as in any color reproduction system, it is first necessary to make a component color analysis of the color of the object or image being televised. This, for example, may be accomplished by passing light from the object or image through red, green and blue filters, respectively. The light through the lters is thereafter utilized to form appropriate component color images by a suit-v able optical system or a photosensitive group of surfaces. Each of the tricolor analytical records thus obtained is scanned to produce three separate signal trains. At the receiver, each of the signal trains is then employed to control the corresponding scanning element to produce component color images. The several component color images are then combined to form an image in substantially its natural color.

This is the so-called additive process, and is utilized here merely by way of illustration. The invention applies as well to four-color additive reproductions, according to the theories oi Zander, Hering and Ladd-Franklin. While the practice of this invention is applicable to television processes wherein the red, green and blue analytical images of a given scene or object are madev in rapid succession,.this invention is particularly applicable and is of great value in methods and systems of the type wherein component color image signals are transmitted simultaneously, and wherein the component color images are also combined simultaneously to form a natural color image.

Although the so-called sequential method of color image transmission requires a narrower transmission band, in this respect it has an advantage over the simultaneous methods and arrangements.

Such advantage, however, is largely offset in the simultaneous arrangement by reason of the fact that the photosensitive surface generating electrical signals'representative of each of the transmitted 1 claim. (cl. ris-5.2)

tricolor images is active continuously. Furthermore, each of the Vphotosensitive surfaces may be given an appropriate spectral sensitivity to the color of the image falling thereon toincrease eiiiciency of the pickup' devices, and perhaps most important of all is that, in the simultaneous methods, relative'displacements between the images resulting from the motion of the subject are completely avoided. The avoidance of relative displacements between the images which occur in a sequential system results in objectionable "action fringes or color margins, which are seen around the edges of moving colored objects.

Therefore, the only important lsuggested advantage of the sequential arrangement Vover the simultaneous system Would'seem to be the relatively narrow transmission band required for the sequential process, as compared to the simultaneous process. 1

It has been found that it is not necessary to transmit the same band width of frequencies for each of the primary colors in order to obtain high definition in reproduced images. `It has been found that the delineatory capabilities of a primary color are determined by the contrast between vthe color of the light projected upon the screen and the Vcolor of the "screen, In the normal reproduction o'f color images, it may be considered that the screen is normally black, consequently'the delineatory capabilities of the blue color on such a screen are less than those of the red image which, in turn, are less than those of the green image. Since the delineatory capabilities determine the definition of an image, it will be appreciated that it is important that all of the frequencies and fine detail of the green image must be faithfully transmitted and re. produced in the receiver. On the other hand. the electrical currents representative of the red image will not reduce the definition of the image noticeably if the higher frequencies are suppressed, and this'is also true to even a greater extent o f the signal currents representative of the blue image.` 'Tests have indicated that at least a 40% reduction in band width of the blue and the red image band of frequencies may be provided without any noticeable change in denition.

It will therefore be seen that the signal channels transmitting the red and the blue information no longer require the same band' width as that'of the green image channel.v

' Advantage has been taken of this fact by A'. N. Goldsmithv in U. S. :Patent 2,335,180, dated No-l vertical direction is transmitted becauserofrtlfref` maintenance of the same number of scanning lines.

According to this invention; an auxiliarysignalv is transmitted in place of the unused detail of the blue component signal channelby'transmiteting the auxiliary signal during alternate or iii-,-

terlaced scanning lines and reproducing the` auxiliary image on a separate reproducing de- In order toA have as properf'understanding: of the operation-` of thisf invention;` it :may: be Well atthis time torefenbrieyrto the theoryofscanning, asemployediir. the develcpm'entzrof teleL vision'images.

'I'he-transmissionrand reproduction ofltelevision images 1 arey accomplished-*by analyzingfthe: vscene or image into itsfimageh elements: whichlareselectedy from the=image=areaf.in"fan alternatewse quence of scanningvfand transnriitted-1 one after another.`V Since the scanning andimagerepeti tionfprocessesare essentially-fartlcial"ones; the number of picture elements and tlieetotalinum`- ber: off-scanningzflines;,the"sequence off-'transmission of 'the-flines: thesaspectratio; Yandv the rate ofimage repetiti'oriwcarmbeechosernarbitrarily;I so long asftheyf. arersimiar*l atbothrthe-transmitter andfreceiverr In the progressive or non-intexslaced pattern; the:4 scanning',J element .moyesratfconstantsspeed tivefline. This v-process; of-rscanninggis ganalogous to; ythe procedure 'employedinfreadingp This fp rocess.4 is vrepeated- .until#thescala/ningE element-reaches the?. bottom ofethe-.l-image. at whichtimevittis quicklyv returned:tcxtlfief upper leitshancl: corner of thefpaget orrimagetofrepeatzthescanninggproce a ess.

The scanning .pattermemployed infthefpractice of `transmission. andreceptionpf television images ismhowever, somewhat .more..-comp licated. It-is designated asi-:thee interlaced`= typeiofscanning and. ,consists of. twos-setsvfof ialter-nateflines The lines must be; spaced fromeach otherybythewidth ottone-.linee and. -`thef-lines.- of one:- set :must-nt ac, curately finto l`thespaces.between :theflines ofthe precedingets; Thefwordaeldf has been see; lectedto -designater-a: scallingpatterrr-composed of: half the.. total. number: of. lines -z-With blank spacesbetween them-.1l TheeWOrdframQl-has 'been designated as the complete scanning pattern; orftwo neldsf,A It-.willi be=seen therefor@that'a-singleeld scanningwill produce fpnly'fhaifffthe: detail, in:thie vertical 'directions It f Will-,f;beeremembered;,how ever; thatV as reductiorrmf one-'haiti` of theav detail oftne; blue f; color.: component `imageiwill.not refi 4 duce the overall detail of the reproduced color image. It is, therefore, possible, without degradation of color image detail, to transmit only one field of each frame of the blue color component image. By appropriate arrangements of elements and switching devices, it is possible, therefore, to transmit additional information during ha1i. of; the scanning time,or,,for example, during-alternatescanning-fields. 'I'hisrmay be accomplished on either the odd or the even scanning lines in the scanning process.

Amrimary object of this invention is, therefore, to produce an improved television system.

Anotherf ob'ject'foff'this invention is to provide -for-a-more'economical employment of frequency spectrum in the transmission of television imalg-Lersz Y Still another object of this invention is to pro- Vide'forY the transmission of additional image information and the likerwithout the employment of'additiona-l'band"width.,. o

Otherf and; incident ai; objects of.: theinvention wiil Ebe; apparent .toi thoseiskilledfgin thefiafrtzfrom a'. reading i of;` the?` following; specification; and f an inspection of the accompanying drawing; in which:

Figure-1 shows rby,l block diagram; one formg of this invention;l

Figure 2 shows# by" detailed circuit-1 diagram; a switching; arrangement; suitableforfy employment inrvarious forms of thisfinvention;v

Figure 3- shows block diagramY 4one form of transmitter employing,w in ,I practieeeone f formtof this invention;- and,`

Figure4ealsogshowsfbyfblocle dia-gramestill ,am otherform aofthisv inventionfaseappiled". toftele: vision-image.piclmprrlevices.v

Turningfnow inrmore detail tojlligfurefzl, therers showna televisionreeenen-arrangement-rcapable ofthe:` reproduction ofi' images.x` in: substantially their naturali; color-,` together with@ an auxiliary imagereproducerr Asradio frequency? ampl-ier vl :selects .thedesired radio frequency-carrierrand-ftransfers energyvto. converter: 3. Theaconverter; produces? fouine: termediate-ffrequency amplierf5 :desiredrband of? intermediate frequenciess. which'` arci furtherL amplified inf separatecamplifiers:v colorrdesignaited asgreenampliiierz'l, redgamplienf andfbluesame plier I I:

Although circuit" arrangements arefwellf fk'nown in thezartl for1 accomplishing theestablishment of separate,` green; red: and' blueaintermediate-free quencies for'thev reproductioniin color television; an improved arrangementisshown,andidescribed in my4 co-pending-U S- application; SerialvN; '760;400,V filed Ju-ly fl 1,' 1947, entitled? Signal "Sepe ara-tor.

Theaseparatencolorfsignalszarestherr appliedffto the. controlelectrodes off theirfrespective.- image reproducing=tubes? or;i kinescopesrt l 3;'Y l 5 and f' I 1;' which ,separatelwreproducef th-efselecteclfcompoanent #colon-images andoformza'.,naturalxcolonime age-.by-superpositioningaofrthefselectedrscompoe nent color? images: One.l suitable rform: thatithe super-position of the selectedrcomponent:color. images -may talref-isfillustrated, for;- eXa-mple',= in thefGol-dsm-itnflatent 2533591.80;f referredatozaboie:

Thegblock :I Siprod-ncesffromthecompositegsigs nalga synchronizinggpulse zfor; deectionwcontrol-,of deflection signal generator 2 I The deflection and'rcontrol` ci-rcuitsrsuitablei'for employmentfin-thepliacticefofi this .z ventio'n are Well-known andidescribedinf-thefU: Si patenttto 'Iolson etz al., v2;101352.0;rdated;Decexrltier 1'7 j ,1987;

or in the U. S; patent to Vance, 2,137,039, dated November 15, 1938. y

Various' electrodes of the electron gun rnot shown indetail in the drawing are to be supplied, as usual, with suitable operating potentials. This may be accomplished as taught in the television art.

synchronizing pulses at field frequency are alsotransmitted through the connection marked control to switching arrangement 23 which may, for example, take the form of the multivibrator arrangement shown in detail in the circuit diagram of Figure 2.

The-function of switch 23 is to alternately switch signals from the blue amplifier II between image reproducing tubes I1 and I9 during alternate scanning fields.

The deflection arrangements for tube I9 are connected to deflection generator 2| in a manner similar to the deflection arrangements for the green, red and blue component image reproducing tubes I3, I5 and I1.

The operation of the switch 23, therefore, causes image reproducing tube I1 and I9 to be operable alternately at field frequency.

It therefore follows that if the blue amplifier IIA furnishes during one field signals representativeof the blue component image, while in the alternate fields furnishes signals representative of an auxiliary image, there will be produced alternately a blues component image in tube I1 and an auxiliary image in tube I9.

Suitable image pickup and transmission arrangements are shown in Figures 3 and 4 and will be described in more detail below.

Turning now in detail to Figure 2, there is shown a circuit diagram suitable to produce the switching necessary in the practice of this invention. The circuitI arangement shown in Figure 2 may be substituted for the block 23 of Figure 1.

The synchronizing signal is applied to the control electrode of tube 25. The synchronizing signal applied to tube 25 will normally be the same as utilized for field deflection control in the television system.

The tube 25 operating in conjunction with tube 21 will produce in the output circuits two square waves, as indicated. It will be noticed that the square wave 29 is 180 out of phase with the square wave 3I. the well-known manner by employing both an anode coupled output and a cathode coupled output to tube 2'I.

The operation of the multivibrator circuit, including tubes 25 and 21, is well known in the art and needs no detailed description here. The particular form of multivibrator illustrated is commonly known as the cathode coupled multivibrator, which produces in its output circuit a square wave whose frequency of recurrence is one-half that of the frequency of the incoming synchronizing pulses.

Square waves 29 and 3l are fed to a control electrode of tubes 33 and 35, respectively. Tubes 33 and 35, together with their associated circuit elements, are of a type whose operation is switchable by application of a potential to one of the control electrodes.

In the circuit arrangement shown, tubes 33 and 35 are alternately operative during alternate eld scannings.

During operation of tubes 33 and 35, a signal is applied to another of their control grids, as illustrated, to be amplified therein. By applying the blue component image signal during alter- This is obtained in r nate field scannings, tube 33, for example, will amplify only the blue image signal, while an auxiliary signal may be substituted for the blue component kcolor image signal during alternate eld scannings to be applied to and amplied in tube 35.

The connections and circuit arrangements shown will, therefore, cause blue image reproducing tube 31 to always receive on alternate neld scannings the blue component signal, while auxiliary image reproducing tube 39 will receive on alternate field scannings only the auxiliary image signal.

Turning now to Figure 3, there is shown by block diagram one form of transmitter suitable' for employment in the practice of this invention. The terms transmit transmitter and transmitting do not contemplate a limitation to the radiant'type of transmission. Once the signals are developed representing each of the color components and with varying degrees of image detail resolution, they may be conveyed or'utilized by any suitable or well known means. rIhis may, for example, be by the radiation of one or more modulated carrier frequencies or by conduction by apparatus such as coaxial cables or other appropriate conducting means. vrIhe terms, therefore, are used in their-broad sense. A suitable television camera 4I, which may, for example, take any of the well known forms, such as those well shown and described inthe article entitled An Experimental Simultaneous Color Television System, beginning on page 861 of the Proceedings of the Institute of Radio Engineers forSeptember 1947, furnishes appropriately designated color component signals to red channel amplifier 43, green channel amplier 45, and switcher 41. The signal applied to switcher 41 by the color television camera 4I is the blue component signal.

Color television camera 4I is synchronized in the well known manner, together with television camera 49, which may, for example, take the form of the popular black and white camera shown and described in the article entitled Image Orthicon Camera by R. D. Kell and G. C. Sziklai, published in the RCA Review for March 1946.

Signals from the television camera 49 are also fed to switcher 41.

A portion of the vertical synchronizing signal energy is applied to switcher 41 to control its frequency of change. Switcher 41 may, for example, take the form shown in detail in the circuit diagram of Figure 2.

In accordance with the explanation given in the circuit diagram shown in Figure 2, the switcher 41 will, during alternate field scannings, pass signals from the color television camera 4I and from the television camera 49 to the blue channel amplifier 5I.

Signals from the red, green and blue channel amplifier 43, 45 and 5I are then passed to the transmitter 53. A suitable transmitter is also shown and described in the article, An Experimental Simultaneous Color Television System, referred to immediately above.

It will be seen that with the arrangements shown in Figure 3, transmitter 53 will transmit not only all the information necessary to produce a complete color image at the receiver, but will also transmit on alternate fields information conerning the image televised by television camera Turning now in detail to Figure 4, another form 1 ofitransmitting: system.' in accordance =withf the practica-of Ytloisfinvention .-is4 zshown by blockdia- Afcolor television .cameraf 55" and a color televisorcamera 51 are'designed and arranged to pick up separate color images.

Due'to-"oheffa'ct,` h'owever, that it is-necessary only to--transmit alternateblue representative signals? during: alternate Y e'lds of i scanning, it is p'ssible'to combine theY blue' representative sig'- nals-froni two independentsystems on one 1 frequen'cy; byalternatelyr sending each ofthe blue elds from separate cameras 55 and 51;

'I'hefcolor 'television camera 55 furnishes component'A color represer-itatvefl signals to fthef ap*-Y prop'riate'redt channel amplifier-V 59, the` green channel-amplierll and-the switcher 6,3, likewis'ethe coloncarriera 5l vfurnishesrepresentative signalsfto the red7 channel 'amplifierv 65,' the. green channel amplie'rrG-'I and theswitcher-GB.

The' switcher-'63 is f controlledV by the7 vertical synchronizingsignalto switch' the blue. channel amplierfalternately between cameras 55' and 51.

Itwillheseerf, th'erefore,-that the radio frequenciesv-employed"inf-transmitter 'Il andY transmitter 135 may "overlapf to the l extent of' sending bothltheirbluevsignalsfion the same radio freqi'rencycliannel, andA thus savingv in two color transmittersfia bandiwidth equivalent-,to the blue signailchannel;Y

` Havingf thus` described'i the invention what Ais-v by interlaced scanning, a rst image reproducing? device adapted to reproduce' a-substantiallyeblue component color`` image from saidfsulostaritiallyv blueA component f color image 'representativel-sig nal train; af-second imagefreprodueing. devices-a; switching; device connected tosaid .h-stfxan-dsec-` ond image reproducing device; means'orfapply ing" to said switching -dev-ice alternately d-uring only alternate field ,fscanningsy said'substantiallaw/z' blue'A component rcolorf image "representative-sig;

nal train and an additional-image.representative' signal `tra-in developed hy;- interlaced` scanning?" Y GERGE-C. S`ZIKV `T narran-ENOES4 CITEDl The following references areofrrecoxd'itl le of this patenti.

UNITED-STATES PATENTS.

Number" Name Dat= Y zssages?.`r Alexandef'sonf :Nova 99.1943' 2,335,180 Gerdsmitn l v Nov yzzisl'e 

